This invention relates generally to the cooling of heat-producing electronic components and, more particularly, to a heat exchanger having fluid control means for deterring the formation of high pressure within the heat exchanger and/or reducing the premature egress of fluid from the heat exchanger caused by the high pressure.
Effective dissipation of heat produced by electronic components is an important concern in optimizing circuitry performance. In addition to optimizing performance, effective heat dissipation also helps to prolong the useful life of those components. Heat dissipation is particularly important in the case of high-power electronic components, such as microprocessors and lasers, which generate a relatively high amount of heat in a relatively small area.
Finding suitable heat exchangers to adequately dissipate the heat generated by these components is a difficult task. These components are typically used in systems housed within a cabinet having a fan mounted in the back. The fan pulls cooling fluid, usually air, across the electrical components mounted within. A suitable heat exchanger should function adequately given this environment. Exotic methods of cooling high-power electronic components, such as forced liquid cooling, are undesirable due to the high cost of implementation and maintenance in these systems. Given their relative simplicity, traditional plate fin heat exchangers are generally preferred from cost and implementation perspectives. These exchangers offer high surface area for heat exchange relative to their size. Nevertheless, often these devices are inadequate to dissipate heat generated from high power electronics, although improvements are being made.
Advances have been made involving the use of narrow channel and micro-channel plate fin heat exchangers to cool electronic components. For example, a patent issued to the applicant, Azar et al., U.S. Pat. No. 5,304,846, discloses a narrow-channeled heat exchanger with certain geometric relations aimed at improving the heat dissipation of the heat exchanger. Specifically, the patent teaches optimal ratios relating the height of the plate fins to the width of the channels. The ratios can be selected to optimize the heat dissipation capabilities of the heat exchanger for a given pressure drop across the heat exchanger.
Although narrow channel heat exchangers significantly improve heat dissipation, they, like all other plate fin designs, suffer from boundary layer formation. The boundary layer consists of hydrodynamic and thermal layers which result from friction or drag between cooling fluid and a plate fin. The layer tends to blanket the plate fin thereby insulating it from the cooler fluid flow. This reduces heat transfer. Additionally, the layer narrows the remaining channel available to fluid flow which further impedes fluid flow thereby compounding the problem. The boundary layer therefore thickens as the fluid progresses down the channel contributing to high pressure within the fin field.
Efforts to reduce boundary layer formation in heat exchangers include irregularities such as protrusions, indentations and louvers along the plate fin surface. These irregularities are intended to disturb the boundary layer to prevent it from building up. From the standpoint of boundary layer disruption, the greatest improvement would be a device having as many irregularities as possible. Unfortunately, however, such an approach leads to practical problems. First, it is difficult, if not impossible, to extrude a plate fin having the desired surface irregularities. Extrusion techniques are limited to producing lengthwise ridges (horizontal and vertical) which have limited ability to disrupt the boundary layer. Other manufacturing techniques such as casting and machining also preclude intricate plate fin textures. Perhaps more important though, increasing irregularities, as described above, also decreases the velocity of the passing fluid within the channels formed by the textured plate fins which tends to increase pressure within the fin field.
The applicant has found that high pressure in the fin field leads to inefficient heat transfer and premature egress of fluid from the fin field. Therefore, a need exists for a flat fin heat exchanger that deters high pressure formation, prevents the premature egress of fluid from the fin field caused by the high pressure, and/or minimizes boundary layer formation without increasing pressure. The present invention fulfills this need.